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Preparation and Characterization of Modified β-Cyclodextrin Polymer Microsphere and Its Adsorption Behaviour for Heavy Metal Ions in Water

Author: YuXiaoXue
Tutor: SunXiaoMei;LiBuHai
School: Central South University for Nationalities
Course: Analytical Chemistry
Keywords: β-Cyclodextrin Polymer Microsphere Pyromellitic Dianhydride Modification Adsorption Heavy Metal Ions
CLC: X703
Type: Master's thesis
Year: 2009
Downloads: 94
Quote: 4
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Abstract

The mine exploit,its processing and utilization,drainage of industry wastewater, landfill of waste and other human activities have polluted extremely serious on water in our country. Traditional or simple method can not deal with the waters polluted by heavy metals effectively now.Therefore,it is the critical time to develop new technologies of raw materials from wide source,low cost and high treatment effection to treat with the waters polluted by heavy metals .Cyclodextrin(CD) is the floorboard of a series of cyclic oligosaccharide produced by the effect of cyclodextrin glucantransferase made by bacillus from amylase. It is a kind of natural compound with wide source.There are a lot of primary and secondary hydroxyls on the surface of CD molecules,so it is easy to do chem-crosslinking and modification with new functional groups to them and broaden the applied area of CD.The sufficient investigation of references home and aboard about the structure characteristics of CD has been studied.Its modification research actualities and treating methods on waste effluents polluted by heavy metals shows that developing a novel adsorbent by using CD as the precursor compound has a great academic significance on the enrichment of adsorbents synthesizing chemistry.Besides,the applications of the proposed adsorbent on practical waste water have certain prospect. Basing on the ideas above,main research work is as follows:1.The preparation and characterization of Pyromellitic Dianhydride(PMDA) modified cyclodextrin polymer microsphereThe cyclodextrin polymer microsphere was synthesized for 2.5h reaction by usingβ-CD as the functional monomer, toluene 2,4-diisocyanate(TDI) as the crosslinker, poly-dimethylsiloxane(PDMS) as the diffusion medium in the solution of dimethyl sulfoxide (DMSO).Then the modification of PMDA onto the surface of cyclodextrin polymer microsphere in N,N-dimethylformamide (DMF) with water bath at 50℃,magnetic stirring for 4h,was performed. The novel adsorbent- PMDA modified cyclodextrin polymer microsphere was therefore obtained.The optimized synthesizing conditions are:1:9.5 molar ratio of the monomerβ-CD to the crosslinker TDI in polymerization reaction,1:2.5 mass ratio of the cyclodextrin polymer microsphere to the modifying compound PMDA in modification reaction.The changes on morphology and particle diameter of the microspheres before and after modification were investigated by scanning electron microscope (SEM) and BET autosorb instrument.Fourier transfer IR (FTIR) spectrametry and X-ray photoelectron spectroscopy (XPS) were used to study the molecular structure and the elements distribution on the surface ofβ-CD microspheres.The changes of the thermal characteristics of the microspheres were measured by differential scanning calorimetry (DSC) .After the modification with PMDA to cyclodextrin polymer microsphere,the SEM picture shows a little increase of the particle diameter.The measured surface areas by BET autosorb instrument are 23.3 and 7.15m2·g-1 for microspheres before and after modification,respectively.The increase of the particle diameter is proved again.In FTIR spectra, a new peak at 1726cm-1 was observed, which should be assigned to the C=O stretching of–COOH on the surface of the modified microsphere, and the -OH adsorption band became wider. The XPS spectra show that the area ratio for the peak at 288.8eV attribute to carboxyl group increases significantly from 6.0 to 16.0% after modification. While the area ratio for C-OH at 286.0eV decreases from 24.0 to 19.0%,they both confirm the existence of abundant carboxyls on the surface of modified microspheres.TG and DTG figures show that the thermal stable temperture drop from 220 to 150℃after being modified by PMDA. And there appears heat sorption in the corresponding temperture region in DSC figures, indicating that the falling off of the small groups on the surface of modified microspheres is decalescence,it also verifies the occurrence of the falling off reaction of the groups.2.The static adsorption behaviour of the novel adsorbent-modified cyclodextrin polymer microsphere for heavy metal ionsThe adsorption behaviour of the proposed novel adsorbent on six common heavy metal ions Pb(II),Cd(II),Cu(II),Zn(II),C(rIII) and N(iII)has been studied.Using static adsorption method,the effects of the main factors,such as dosage of adsorbent,concentration of metal ions,acidity of the water solution and adsorption reaction time on adsorption capacity have been investigated and optimized. Because of the existence of abundant carboxyl groups on the surface of the adsorbent,its adsorption properties are greatly affected by the acidity of the solutions. In the low pH range,the concentration of proton is high and the metal ions are present in solution as free cations, so that protons can compete with cations,leading to low adsorption capacities for the metal ions.In the range of pH5.0~6.5,the adsorption capabilities to the six metal ions reach maximum,respectively.Then there appears plateau in acid curve.The proposed adsorbent has its maximum capacities on every metal ion .Once it saturated,the adsorption capacities will no longer improve with the increase of the adding concentration of the metal ions. All adorption balance time of this adsorbent to the six metal ions are very short.It indicates that the adsorption efficiencies are comparatively high.When the adsorption time are fixed for 20min,at the optimum pH of each metal ion,the maximum adsorption capacities of the novel adsorbent to Pb(II),Cd(II),Cu(II),Zn(II),C(rIII),N(iII)are 132.6,87.3,68.74,56.29,54.35,31.05 mg·g-1,respectively.Compared with the microspheres before modified,there are remarkable enhancement.3. The adsorption mechanism ofβ-CD cyclodextrin polymer microsphere for heavy metal ionsApplying the adsorption experimental data to pseudo-first-order and pseudo-second-order dynamics equations separately, the results show that the adsorption behaviour for six metal ions conform to the pseudo-second-order dynamics equation better, confirming that the adsorption process is controlled by chemical sorption. The adsorption isotherms of the metal ions on the modified microspheres indicate that Langmuir isotherm equation gives better fit than Freundlich isotherm,confirming that the adsorption for the metal ions is monomoleculay layer form. The absorbents loaded with the metal ions have been analysed by FTIR and XPS. The results show that the carboxyl modified onto the surface of the cyclodextrin polymer microspheres is the main functional group for the novel adsorbent. Carboxyl groups play a very important role in the adsorption reaction.4. The regeneration and application of the modified cyclodextrin polymer microsphere adsorbentThe regeneration of the adsorbents could be implemented by 0.2 mol·L-1 HCl or 1.0 mol·L-1 H2SO4 with first-regeneration ratios>90% and most second-regeneration ratios>80%,respectively. After applying this adsorbent to the treatment of industrial effluent containing Pb(II),which can fit the Integrated Wastewater Discharge Standard (GB 8978-88)(<1.0 mg·L-1).The same results could be obtained after regeneration for three times.

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